Search Results (106)

FeCrAl exhibits excellent resistance to high temperatures, corrosion, and irradiation, making it a prime candidate material for accident-tolerant fuel (ATF) cladding. This study investigates the high-temperature creep behavior of FeCrAl alloys with grain sizes of 12.0 μm and 9.9 μm under temperatures ranging from 450 °C to 650 °C and applied stresses between 75 and 200 MPa. The texture, grain morphology, grain orientation, and dislocation density of FeCrAl were characterized by electron backscatter diffraction (EBSD). The results indicate that temperature, applied stress, and grain size are the primary factors governing high-temperature creep behavior. The material texture showed no significant difference before and after creep. Large grains tend to engulf smaller ones during the creep process at lower temperatures and stresses, reducing the proportion of low-angle grain boundaries (LAGBs). In contrast, at higher temperatures or under higher stress, dislocations proliferate within grains, leading to a significant increase in the number of LAGBs. As the applied stress increases, the dominant creep mechanism tends to convert from grain boundary sliding to dislocation motion. Moreover, higher temperatures or smaller grain sizes lower the critical stress required to activate dislocation motion and significantly increase dislocation density, severely degrading the creep resistance. Full article

Room-temperature rotary swaging was conducted on microalloyed high-ductility Mg-0.7Sm-0.3Zr alloy rods to investigate microstructural and mechanical variations across different swaging passes and radial positions. The results indicate that following room-temperature rotary swaging, the alloy rods exhibit a large number of tensile twins and low-angle grain boundaries, leading to significant grain refinement. After two swaging passes, the microstructure exhibits a pronounced radial gradient, characterized by progressively finer grain sizes from the core to the edge regions, with a hardness difference of 3.8 HV between the edge and the core. After five swaging passes, the grain size was refined from an initial 4.37 μm to 2.02 μm. The yield strength and ultimate tensile strength of the alloy increased from 157 MPa and 210 MPa in the extruded state to 292 MPa and 302 MPa, respectively. This observed strengthening is primarily attributed to grain refinement, dislocation hardening, and texture strengthening, with grain refinement playing the dominant role. The grain refinement process during rotary swaging can be divided into two stages: in the initial stage, coarse grains are subdivided by tensile twinning; in the later stage, high-stress-induced grain boundary bulging leads to new dynamic recrystallization, further refining the microstructure. Full article

To address the issue of surface grain coarsening in laser-induction hybrid phase transformation of 42CrMo steel, this study investigated the effects of four pretreatment processes (quenching–tempering (QT), laser-induction quenching (LIQ), laser-induction normalizing (LIN), and laser-induction annealing (LIA)) on the austenite grain size and wear resistance after laser-induction hybrid phase transformation. The results showed that QT resulted in a tempered sorbite structure, resulting in coarse austenite grains (139.8 μm) due to sparse nucleation sites. LIQ generated lath martensite, and its high dislocation density and large-angle grain boundaries led to even larger grains (145.5 μm). In contrast, LIN and LIA formed bainite and granular pearlite, respectively, which refined austenite grains (78.8 μm and 75.5 μm) through dense nucleation and grain boundary pinning. After laser-induction hybrid phase transformation, all specimens achieved hardened layer depths exceeding 6.9 mm. When the pretreatment was LIN or LIA, the specimens after laser-induction hybrid phase transformation exhibited surface microhardness values of 760.3 HV0.3 and 765.2 HV0.3, respectively, which were 12 to 15% higher than those of the QT- and LIQ-pretreated specimens, primarily due to fine-grain strengthening. The friction coefficient decreased from 0.52 in specimens pretreated by QT and LIQ to 0.45 in those pretreated by LIN and LIA, representing a reduction of approximately 20%. The results confirm that regulating the initial microstructure via pretreatment effectively inhibits austenite grain coarsening, thereby enhancing the microhardness and wear resistance after transformation. Full article

Marine engineering thick plates are essential structural materials for large vessels and offshore platforms, and optimizing their manufacturing processes is critical for advancing marine equipment. This study examined the microstructural and property variations in 120 mm-thick S460 plates fabricated by thermo-mechanical controlled processing (TMCP). A finite element model was developed to simulate the cooling phase, enabling the prediction of the internal cooling path in the thick plate. An optimized cooling scheme was proposed, which was validated against the model and implemented. The following key results were obtained: (1) Under the initial cooling parameters (initial temperature: 715 °C, duration: 130 s), the 60 mm depth toughness was severely compromised, as evidenced by a low −40 °C impact energy of 59 J, significantly lower than values observed at the10 mm and 30 mm depth positions. Microstructural analysis revealed that the 60 mm depth region was dominated by ferritic bainite and pearlite, with a pearlite content of 8.7%. Numerical simulations further indicated a 60 mm depth cooling rate of 1.10 °C/s under these conditions. (2) Model predictions confirmed the original 60 mm depth cooling rate of 1.10 °C/s. The optimized process increased the initial cooling temperature to 725 °C and extended the cooling time to 160 s, achieving an enhanced 60 mm depth cooling rate of 1.36 °C/s. (3) The optimized process remarkably improved the 60 mm depth impact energy to 144 J, achieving near-complete elimination of pearlite, increased granular bainite content, refined M-A constituent size, and enhanced density of high-angle grain boundaries. This study demonstrates that enhancing internal temperature gradients and prolonging cooling durations can effectively inhibit microstructural degradation in 60 mm depth regions of thick plates, providing both theoretical foundations and practical methodologies for optimizing TMCP processes of extra-thick steel plates. Full article

A novel Ti-N-O composite was prepared by powder nitriding/oxynitriding combined with the spark plasma sintering (SPS) method. The effects of N/O on the microstructure and mechanical properties of the Ti-N-O alloy were systematically studied. The results showed that the addition of N/O elements significantly improved the mechanical properties of commercially pure titanium (cp-Ti). The hardness reached 298.8 HV0.1 while the yield strength can reach 666 MPa. And, the O element played a leading role in regulating the microstructure and morphology of the Ti-N-O alloy. With the addition of the O element, the microstructure showed an equiaxed structure, and the characterization showed that this region is an O-enriched region, and that a small amount of nano-TiO₂ particles appeared in the alloy, which together led to the change in the microstructure. At the same time, more large-angle grain boundaries were generated in the Ti-N-O alloy. This study investigated a new method for the preparation of titanium materials and provides new ideas for researching medical titanium materials. Full article

In this study, we investigated the two-phase hardening behavior and microstructural evolution of S32750 duplex stainless steel during the tensile deformation process. The analysis was conducted using in situ electron backscatter diffraction (EBSD), scanning electron microscopy (SEM), and microhardness testing. It was observed that strain transfer occurred between the two phases in the position away from the fracture. The ferrite phase exhibited softening, while the austenite phase underwent hardening. In the region less than 1 mm from the fracture site, both phases experienced a rapid hardening, with the maximum hardness difference between the two phases near the fracture reaching approximately 45 HV. In situ EBSD results indicate that the kernel average misorientation (KAM) value for the ferrite phase consistently exceeds that of the austenite phase during the initial stages of deformation. Conversely, in the final stages of deformation, the KAM value for austenite surpasses that of ferrite. In the initial stage of deformation, the type of grain boundaries in both phases remains largely unaltered. However, in the later stages of deformation, there is a marked increase in the number of small-angle grain boundaries within ferrite, which become approximately three times that of the large-angle grain boundaries. As deformation progresses, the maximum orientation distribution density of the ferrite phase is reduced by approximately 50%, with the preferred orientation shifting from the {100} plane to the {111} plane. In contrast, the orientation distribution of the austenite remains relatively uniform, with no significant change in the maximum orientation distribution density observed. This indicates that after substantial deformation, the rotation of ferrite grains significantly increases the deformation resistance, whereas the austenite phase continues to harden. This differential behavior leads to the continuous accumulation of strain at the phase boundaries, ultimately causing cracks to form at these boundaries and resulting in the sample’s fracture. Full article

Grain boundary engineering (GBE) has been widely used to modify grain boundary (GB) networks to improve GB-related properties in polycrystalline materials. With the development of miniaturized and lightweight terminal connectors comes a greater demand for phosphorus bronze. A fine grain size and excellent GB characteristics are the keys to synergistically enhancing mechanical strength and bending workability. In this study, the effects of the annealing temperature on the grain boundary character distribution (GBCD) optimization and the bending properties of phosphorus bronze were studied by means of electron backscatter diffraction and a 90° bending test. The results show that the deformed microstructure of the as-received material recrystallizes upon annealing at 400 °C for 1 h. The average grain size is 1.6 μm, and a large number of special boundaries (SBs) are present, accounting for 71.5% of all GBs. Further, the incoherent Σ3, Σ9, and Σ27 boundaries are the most abundant, effectively disrupting the network connectivity of random high-angle grain boundaries. The grain size gradually increases with the annealing temperature increase. The fractions of the Σ9 and Σ27 boundaries gradually decrease. Although the proportion of SBs further increases at higher temperatures, most SBs at these temperatures are coherent Σ3 boundaries that do not contribute to the direct optimization of GBCD. Moreover, in the absence of a significant difference in tensile strength, the GBCD-optimized fine-grained sample demonstrates smooth surfaces without orange peel effects when bent at 90° with R/t = 0 in the bad way. This improvement is attributed to the uniform deformation of fine grains and special boundaries, which enhances the bending workability of the GBCD-optimized fine-grained strips. Full article

Pulsed detonation–plasma technology (PDT) is a surface-modification technology used in an atmospheric environment, where plasma, a detonation impact and thermal conditions are combined and have an effect on the material’s surface. In this study, annealed 65Mn steel was selected to further study the principle of PDT modification. The results show that the modified layer with fine grains was divided into an infiltration layer with a large amount of non-uniformly distributed granular CW₃ carbides and a heat-affected layer below the infiltration layer after PDT treatment. However, a higher amount of acicular martensite and a lower amount of austenite was achieved in the modified layer, containing a large number of small-angle grain boundaries, dislocations, and twin grains. After the PDT treatment, the hardness of the modified layer, heat-affected layer, and substrate was 980 HV, 856.2 HV, and 250 HV, respectively. The mass loss of the sample before and after PDT treatment was 21.1 mg and 12.4 mg, respectively. The hardness and wear resistance of the modified layer were greatly improved compared with the substrate because of the combined effect of the solid-phase transformation, element infiltration, and distortion. Full article

Based on the flexible adjustment of the seven-wire, this study will assemble a new toughened seven-wire which is combined with a common single welding wire and the existing welding wire containing ductile alloy element (Ni element), and the microstructure properties, mechanical properties and toughening mechanism of the welding seams were studied. The results show that the microstructure of the four combinatorial seven-wire welding seams is mainly composed of coarse proeutectoid ferrite (PF) and fine acicular ferrite (AF). Among them, the core of inclusions that induce AF nucleation and growth are mainly composed of Al, Ti, Si, and Mn-based oxides, and the edge of inclusions is mainly composed of Mn and Cu sulfides (MnS, CuS). The addition of Ti compounds further promotes AF nucleation. This is also a reason why the impact toughness of the combinatorial seven-wire W2/W3 welding seams is higher than that of other combinatorial seven-wire welding seams, but the impact toughness of the rich Ni seven-wire can meet the standard requirements of the China Classification Society (CCS). Among the four combinatorial seven-wire welding seams, the proportions of large angle grain boundaries (grain orientation difference ≥ 15°) that improve the ability of materials to prevent brittle fracture are 65.9%, 68.8%, 66.0%, 61.7%, respectively, that is, the larger proportion of large angle grain boundaries in combinatorial seven-wire W2 welding seams (Ni content is 0.0897%) is one of the reasons for the higher impact toughness of the welding seams. With the increase of Ni content in the welding seam, the AF content first increased and then decreased, the yield strength and tensile strength increased, and the elongation and section shrinkage first increased and then decreased. When the combinatorial seven-wire W2/W3 was used, the welding seam plasticity was the best. Full article

To address anisotropy challenges in electric arc-based additive manufacturing of Inconel 718 alloy, this study develops a novel wire feeding oscillated double-pulsed gas tungsten arc welding additive manufacturing method (DP-GTA-AM) enabling precise thermal-mass transfer control. Series of crack-free thin-walled Inconel 718 alloy parts were successfully obtained by this proposed approach, and the microstructure and mechanical properties of the parts were thoroughly studied. The results indicate that the microstructure changes from dendrites and cellular crystals in the bottom to equiaxed grains in the midsection and entirely equiaxed crystals in the top, resulting in notable grain refinement. With an average grain size of 61.76 μm and an average length of 83.31 μm of large angle grain boundaries, the density of the <001> direction reaches 19.45. The difference in tensile strength and ductility between the horizontal and the vertical directions decreases to 6.3 MPa and 0.38%, which significantly diminishes anisotropy. Fractographic analysis confirms quasi-cleavage failure with homogeneous dimple distribution, demonstrating effective anisotropy mitigation through controlled solidification dynamics. Full article

Invar alloy has a wide range of applications in aerospace and precision instruments. However, the microstructure evolution during rapid solidification is not yet fully understood. In this study, the rapid solidification microstructure of Invar alloy with undercooling ranging from 5 K to 231 K was investigated using optical microscopy, EBSD, and TEM techniques. The results show that, as the undercooling increased from 5 K to 181 K, the microstructure transitioned from large dendrites to columnar grains and finally to small equiaxed grains. When the undercooling ranged from 181 K to 193 K, the grain size suddenly increased before continuing to decrease with further undercooling. EBSD analysis revealed that, for ΔT > 181 K, two distinct types of grains appeared in the microstructure: one larger and the other much smaller. Under low undercooling conditions, the grains grew anisotropically with a preferred orientation, while under high undercooling, there was no apparent preferred growth orientation. Many twin boundaries were observed in the high-undercooling samples, which were further confirmed by TEM analysis. Additionally, both twin boundaries and high-angle grain boundaries increased gradually with undercooling. Full article

This study investigates the evolution mechanisms and electrochemical corrosion behavior of laser-welded joints (WJs) between 6063 and 6082 dissimilar aluminum alloys under varying welding powers. The analysis focused on the microstructure of the weld metal zone (WMZ), its grain boundary (GB) features, and its electrochemical corrosion properties. Data from the experiments indicate that a higher laser power (LP) leads to an increase in grain size within the WMZ. At an LP of 1750 W, the weld surface exhibits the poorest corrosion resistance, while other parameters show a relatively better resistance. Additionally, electron backscatter diffraction tests indicate that the high-angle GB fraction on the 6063-T6 side of the heat-affected zone exhibits a substantially reduced measurement compared to the 6082-T6 side. The corrosion form in the WMZ is intergranular, with energy-dispersive spectroscopy (EDS) scans revealing that the poor corrosion resistance is primarily due to the presence of a large amount of Mg₂Si phase. Full article

Fiber metal laminates (FMLs) are a novel lightweight composite material, predominantly utilized in the aerospace sector for large-scale components like skin panels and fuselages. However, research on FMLs in the microsystem domain remains limited. Additionally, they are influenced by scale effects, rendering macroscopic forming theories inadequate for microforming applications. The application of ultra-thin fiber metal laminates in the microsystem field is hindered by this constraint. This paper investigates the friction performance of ultra-thin TA1 titanium alloy/carbon fiber-reinforced plastic (CFRP) laminates at the microscale. The content of the epoxy resin used is 38.0 ± 3.0%. Friction tests on ultra-thin TA1/CFRP laminates were conducted based on the Striebeck friction theory model. The effects of factors such as the weaving method, ply angle, normal force, tensile speed, and temperature on friction performance are explored in the study. Furthermore, the influences of geometric scale and grain scale on friction performance are examined. Geometric scale effects indicate that an increase in laminate width leads to an increase in the friction coefficient. Grain-scale effects demonstrate that as grain size increases, the friction coefficient also increases, attributed to reduced grain boundaries, increased twinning, and increased surface roughness of the metal. Finally, surface morphology analysis of the metal and fiber after friction tests further confirms the influence of grain size on the friction coefficient. Through detailed experimental design, result analysis and graphical representation, this paper provides a scientific basis for understanding and predicting the friction behavior of ultra-thin TA1/CFRP laminates. Full article

A380-Yb (Ytterbium) alloy was prepared by the ultrasonic melting casting method, and effects of hot extrusion on the microstructure and wear properties of the alloy were studied. The results indicate that the addition of rare earth Yb can refine the microstructure of the matrix alloy. After hot extrusion (extrusion ratio of 22.56) of the as-cast A380-Yb alloy, the secondary phase in its microstructure was further refined and the distribution became more uniform. EBSD (electron backscatter diffraction) organizational analysis shows that the average GND (geometrically necessary dislocation) density of extruded rare earth aluminum alloy is significantly increased, by 16.5 times that of the cast matrix alloy. In addition, there are a large number of grains parallel to the <111> orientation and <001> orientation in the extrusion direction. The alloy undergoes dynamic recrystallization during hot extrusion, and the proportion of small-angle grain boundaries is significantly reduced. Under the same friction and wear conditions, the wear rate and average friction and wear coefficient of the extruded rare earth aluminum alloy are relatively small, reduced by 53.8% and 42.6%, respectively, compared to the cast matrix alloy. Its wear mechanism is mainly abrasive wear and slight plastic deformation. In addition, the study also found that under fixed other wear conditions, as the friction speed increases, the wear rate of the extruded rare earth aluminum alloy shows a trend of first decreasing and then increasing. However, with the increase in load, its wear rate gradually increases, and the change in wear morphology is consistent with the trend of wear rate. When the wear rate is high, the wear mechanism of the extruded aluminum alloy is mainly delamination wear and adhesive wear, and is sometimes accompanied by severe plastic deformation. When the wear rate is low, its wear mechanism is mainly abrasive wear. Full article

In order to gain insight into the unique characteristics of manufacturing large-scale products with intricate geometries, experimental nozzle-shaped samples were created using wire-feed electron beam additive technology. Bimetal samples were fabricated from nickel-based alloy and copper. Two distinct approaches were employed, utilizing varying substrate thicknesses and differing fabrication parameters. The two approaches were the subject of analysis and comparison through the examination of the surface morphology of the samples using optical microscopy, scanning electron microscopy, and X-ray diffraction analysis. It has been demonstrated that the variation in heat flux distributions resulting from varying the substrate thicknesses gives rise to the development of disparate angles of grain boundary orientation relative to the substrate. Furthermore, it is demonstrated that suboptimal choice of the fabrication parameters results in large disparities in the crystallization times, both at the level of sample as a whole and within the same material volume. For example, for the sample manufacturing by Mode I, the macrostructure of the layers is distinguished by the presence of non-uniformity in their geometric dimensions and the presence of unmelted wire fragments. In order to characterize the experimental nozzle-shaped samples, microhardness was measured, uniaxial tensile tests were performed, and thermal diffusivity was determined. The microhardness profiles and the mechanical properties exhibit a higher degree of strength than those observed in pure copper samples and a lower degree of strength than those observed in Inconel 625 samples obtained through the same methodology. The thermal diffusivity values of the samples are sufficiently close to one another and align with the properties of the corresponding materials in their state after casting or rolling. The data discussed above indicate that Mode II yields the optimal mechanical properties of the sample due to the high cooling rate, which influences the structural and phase state of the resulting products. It was thus concluded that the experimental samples grown by Mode II on a thinner substrate exhibited the best formability. Full article